Documented the up key shortcut
## What does this MR do?
Documents the `up` key edit note shortcut in the `/help/_shortcuts.html.haml` help pane and the `/doc/workflow/shortcuts.png` screenshot.
## Are there points in the code the reviewer needs to double check?
The issue and MR shortcuts should be merged, they're the same? Shall I open an issue or include here?
This panel also need to be a little more responsive. Shall I open an issue or include here?
Additionally, I have some conflicts regarding the screenshot. This screenshot also needs to update for !4570.
## Why was this MR needed?
Everyone should know about this awesome shortcut.
## What are the relevant issue numbers?
Closes#18114.
## Screenshots (if relevant)
View the [updated screenshot](e7221ad66e/doc/workflow/shortcuts.png)
## Does this MR meet the acceptance criteria?
- [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- [x] [Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md)
- [ ] API support added
- [ ] Tests
- [ ] Added for this feature/bug
- [ ] All builds are passing
- [x] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [x] Branch has no merge conflicts with `master` (if you do - rebase it please)
- [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)
See merge request !4758
1147f6406f
